Start working on virtual consoles/TTYs.

This is a mess right now, but I'd rather commit as I go.

Kernel/Keyboard.h

@@ -6,11 +6,21 @@
 #include <VirtualFileSystem/CharacterDevice.h>
 #include "IRQHandler.h"
 
+class KeyboardClient {
+public:
+    virtual ~KeyboardClient();
+    virtual void onKeyPress(byte) = 0;
+};
+
 class Keyboard final : public IRQHandler, public CharacterDevice {
 public:
+    static Keyboard& the() PURE;
+
     virtual ~Keyboard() override;
     Keyboard();
 
+    void setClient(KeyboardClient*);
+
 private:
     // ^IRQHandler
     virtual void handleIRQ() override;
@@ -20,6 +30,7 @@ private:
     virtual ssize_t write(const byte* buffer, size_t) override;
     virtual bool hasDataAvailableForRead() const override;
 
+    KeyboardClient* m_client { nullptr };
     CircularQueue<byte, 16> m_queue;
     byte m_modifiers { 0 };
 };